The purpose of this proposal is to evaluate the effectiveness of a specific intervention (Responsivity and Prelinguistic Milieu Teaching: RPMT) on improving social communication and motor imitation skills in young children with autism. Both the full RPMT, and the Prelinguistic Milieu Teaching component, have been effective in increasing several aspects of social communication in a group of children with developmental delays and in 3 children with autism. The proposed dependent variables are (a) intentional communication, (b) communication with eye contact, (c) initiating joint attention, (d) coordinated use of the behaviors most frequently used to convey initiating joint attention, (e) attention to positive affect sharing, (e) motor imitation, and (f) expressive vocabulary level. We will test whether treatment effects on these dependent variables vary as a function of (a) pretreatment child and parental characteristics and (b) several characteristics of non-project treatment involvement. We will also test whether treatment effects on 6- month follow-up expressive vocabulary occur and are mediated by initiating joint attention. To control for exposure to situations that evoke communication and to the testing location, a contrast treatment will be used. Children will be randomly assigned to treatments. Children will be randomly assigned to treatments. Children in each treatment will be seen an equal number of times for 6 months. Assessments of communication, vocabulary, and motor imitation will occur at the pre-treatment, port-treatment, and 6 month follow-up periods. Examiners and coders will be blind to treatment assignment.